1. Field of the Invention
The present invention relates to a method of controlling operation of an internal combustion engine by detecting an amount of intake air introduced into the internal combustion engine and controlling the internal combustion engine based on the detected amount of intake air.
2. Description of the Related Art
Internal combustion engines that have been used on motor vehicles or the like have intake pipes for introducing intake air into the cylinders, which provide combustion chambers and intake valves mounted in respective intake ports, and to which the respective intake pipes are connected, for selectively bringing the cylinders into and out of communication with the respective intake pipes. When the intake valves are opened, intake air is introduced through the intake pipes into the cylinders.
The intake pipes are connected to a throttle valve for regulating the rate of intake air (amount of intake air) flowing through the intake pipes. The throttle valve has a valve opening thereof adjusted to regulate the amount of intake air being introduced into the cylinders. An air flow sensor for measuring or detecting the amount of intake air flowing through the intake pipes is disposed upstream of the throttle valve. A surge tank is connected to the intake pipes downstream of the throttle valve and has a pressure sensor for detecting the air pressure in the intake pipes.
A detected signal from the air flow sensor is output to a control circuit, which calculates the amount (mass or volume) of intake air being introduced into the cylinders from the detected signal from the air flow sensor. Then, the control circuit calculates an optimum amount of fuel to be injected into the cylinders depending on the operating state of the internal combustion engine based on the calculated amount of intake air. The control circuit then outputs a control signal representing the calculated optimum amount of fuel to a fuel injector, thereby controlling operation of the fuel injector. For further details, see Japanese Laid-Open Patent Publication No. 2004-190591, for example.
According to the conventional control system disclosed in Japanese Laid-Open Patent Publication No. 2004-190591, when the throttle valve is quickly opened to accelerate the motor vehicle quickly, intake air for filling the surge tank connected to the intake pipes is introduced into the intake pipes, in addition to the intake air that is actually introduced into the cylinders. Therefore, the amount of intake air that is detected by the air flow sensor is the sum of intake air actually introduced into the cylinders and a portion of the intake air filling the intake pipes.
The pressure sensor, which is disposed downstream of the throttle valve separately from the air flow sensor, detects the pressure of intake air filling the intake pipes, and the control circuit estimates the amount of intake air filling the intake pipes. The control circuit is required to subtract the estimated amount of intake air from the total amount of intake air detected by the air flow sensor, thereby estimating the amount of intake air that is actually drawn into the cylinders, for controlling the internal combustion engine.
With the above conventional control system, however, the amount of intake air drawn into the cylinders is estimated based on the amount of intake air detected by the air flow sensor disposed upstream of the throttle valve and the pressure detected by the pressure sensor. Consequently, the control system fails to accurately recognize the amount of intake air actually introduced into the cylinders, which makes it difficult to accurately control the amount of fuel injected into the cylinders based on the amount of intake air.